I have to disagree here. 120ga wheels are an absolute pain to gather and maintain all of the spokes clutched together. The weight means your wrists will need more rest breaks, unless you have some sort of specialized stand I suppose. The more times you go to set that wheel down, the more chances there are for entanglement and frustration....and painted rim scars!
The method I've adopted in the last 6 months or so is to load one inner flange fully, plus a single spoke in the same flange on the outside, use that single spoke to start at the valve stem. Choose cross direction based on LH or RH drilling, twist the hub accordingly, count back 3 or 4 cross and set(install) one of your inner flange spokes. Finish setting the first inner flange, then load your other inner flange based off of LH or RH drilling and single outer flange spoke you installed first. Finish setting that inner flange and you have a mostly stable wheel to work with for installing the rest of the spokes. At least the hub doesn't wobble wildly...and the rest of your spokes are practically going to lay where they need to go. If you have left the nipples moderately loose, you can load one outside flange at a time with no worries of entanglement and having to remove a spoke to get one in. Leaving them loose allows you to get the spoke head under the others with the right aim and a slight pull of the first crossed spoke. Loading them a flange at a time gives your wrists a break and prevents scratches from having too many spokes flopping around in the way. I think I've started doing it this way because I've been doing more drum/Multispeed hubs that don't allow you to fan them down into a single clutch...plus holding onto that extra weight gets tiring and frustrating.
Even the small flange 4 cross New Departure Hubs seem to be easy enough to pop heads under their first crossed spoke. Maybe this is an issue on thicker aluminum flanges?
LOL, We do not disagree! The very best method is the one that works for you. There's no right, or wrong way here.
One thing that being old allows is to look back and adopt the way's that were easier. Old guys are not lazy, we just have figured out how to "get'r done, with the least amount of energy spent".
After high school, I worked for a Ford Dealer as a mechanic. I would watch, observe the old mechanics, and ask questions about their unique methods. Nothing is actually new, it's just different ways, ideas, and methods copied from those that traveled the trail before us. if it's works for you great use it, I'm not charging any royalties. If the way/method does not help, make your repair better/faster/easier just pass and forget it.
Here's some more wheel building ideas for you to ponder.
You do not want to hold the hub after all of the spokes have been dropped into it. It's heavy, and also cumbersome. You want to have a dedicated work area to build your wheels. This could be a dedicated work bench like would be used in a bike shop. Or it could be as simple as a nice clean three-foot square piece of 3/4" plywood. You are going to drill a hole in this surface for the hub axle to sit. In fact, you might want to drill a couple of holes. One the allows a 27" wheel to hang off the edge three inches. The next axle hole would be closer to the edge and allow a 20" wheel to hang off of the edge three inches. If building chrome plated steel wheels just use the work surface "as is", but if building anodized aluminum, or painted rims, just lay a towel on the work surface before you set the loaded hub down for protection. I had my wheel building bench built with a piece of hard Masonite surface that did not scratch. A piece or Wilsonart Laminate would work great. Some guys I know would set the flat board on top of a garbage can so they could sit in a chair while building.
When BMX was just starting in the early 1970's, lightweight was not a consideration. We built hundreds of 20" steel Araya/Ukai, 36 hole, 105 GA, heavy duty wheels for BMX conversions and frame up builds. Most of these were with Bendix coaster brakes. It was necessary to figure out any short cut in build time savings.
If anyone is interested, there are ways to save build time using short cuts in spoke pull up before you begun the actual truing step. If you "pull up" the wheel correctly, it's 90% trued before you even put it on the truing stand and turn a wrench.
We would build our rear "off set" derailleur wheels with different length spokes in each flange to help with pull up and truing. Lots of little time saving tricks, but none of them are actually new, just ideas passed on by old guys. If it helps you great, if not we still don't disagree.